Metallurgist最新文献

The impact of selective laser melting (SLM) process parameters on the porosity, microstructure, phase and chemical composition, texture, and physical-mechanical properties of orthorhombic titanium aluminide Ti₂AlNb (O-alloy) powder was studied using a range of methods, including hydrostatic weighing, scanning and transmission electron microscopy, X‑ray diffraction analysis, energy-dispersive X‑ray spectroscopy, microindentation, and compression testing. It was demonstrated that an increase in the volumetric energy density within the range of 28 to 139 J/mm³ led to the following effects: 1) increase in the relative density of the obtained O‑alloy from 97 to 99.9%, 2) intensification of axial texture with a pronounced 001 direction in the detected β/B2-solid solution, and 3) reduction in the Al content, increase in the Nb content, and lower enrichment with oxygen in the obtained samples. It was demonstrated that detachment from the build platform and longitudinal cutting of the O‑alloy results in the imbalance of residual stresses in samples synthesized on a platform, pre-heated at 200 °C, which is accompanied by the formation of cracks. This study considers the typical structural defects of the alloy, including pores, lack of fusion, and chemical heterogeneity, which are observed following SLM. A series of physical-mechanical properties of the synthesized O‑alloy samples were determined, including Vickers hardness (390–430 HV), elastic modulus (91–98 GPa), compressive yield strength (1060–1080 MPa), and compressive strain (of at least 30%). The relationship between these properties and the structural-textural state of the obtained O‑alloy samples is discussed.

The current stage of development in metallurgy is characterized by unprecedented attention to reducing CO₂ emissions. Replacement of carbon with hydrogen in smelting of cast iron is a method of reducing CO₂ emissions; however, the production of hydrogen is also associated with CO₂ emissions. The carbon monoxide utilization rate during indirect reduction in a blast furnace is 28–38%, in contrast to direct reduction, in which the utilization rate is more dependent on contact area between the reducing agent and oxides. Use of ore-coal briquettes is a promising direction for increasing the utilization rate of the reducing power of carbon in a blast furnace. The study investigates the efficiency of using ore-coal briquettes in production of vanadium cast iron from the perspective of reducing CO₂ emissions. We show that carbon consumption for direct reduction of titanium-magnetite concentrate is six times lower than for indirect reduction. Using ore-coal briquettes in blast furnace charge can reduce the specific fuel carbon consumption in production of vanadium cast iron, which will reduce CO₂ emissions.

The work presents the results of the corrosion resistance study of composite coatings obtained by cold spraying of the aluminum and boron carbide powder mixture on the surface of 08Cr18Ni10Ti austenitic steel. Their chemical and phase compositions, macro- and microstructure, as well as the effect of subsequent heat treatment are analyzed. It is shown that the corrosion of coatings in a 2% boric acid solution at 60 °C is accompanied by an increase in the sample mass and the formation of an aluminum oxide layer. The minimum mass change was observed in case of the coating heat treated at 400 °C, while an increase in heat treatment temperature leads to the intensification of corrosion destruction.

This article studies the process of laser alloying of aluminum and alloy AL25 with metals: nickel, chromium, niobium, in a melting regime. Choice of metals for the study is made according to the criterion of efficiency of melt zone filling under laser treatment. Theoretical analysis of possible intermetallic phases within Al–Ni, Al–Cr, Al–Nb systems is performed, including physical parameters and crystallographic characteristics. Experimental studies by methods of metallography and X-ray diffraction analysis allows establishment of the spectrum of phases formed during alloying of aluminum from powders of these elements. They include both aluminum-rich intermetallics, and chemical compounds enriched with alloying metal. Alloying with niobium disilicide is also investigated to reveal differences in mechanisms of introducing chemical compounds into a laser-affected zone. On alloying with NbSi₂ particles get into the melt zone directly from the powder (a mechanism of particle “flight”), and when alloying with pure metal intermetallic formation of occurs in situ during crystallization. On the basis of calculating the change in lattice spacing of aluminum the concentration of alloying metals within supersaturated solid solution is estimated. The increase in microhardness of alloying zones due to solid solution hardening and dispersion strengthening by intermetallic particles is established.

Systems theory can be used not only to assess the existing state of engineering and technological systems, but also to forecast their development. This approach implies the creation of a generalized model of the object under study taking the existing connections between its individual components into account, along with an analysis of the energetic, material, and informational resources inherent in this object. This allows selection of the most optimal solution for improving the technological system under analysis from a variety of possible options. Creation of high-entropy compounds of various compositions is an intensively developing direction of modern materials science. Due to their specific chemical composition, such materials may exhibit a unique combination of properties, thereby outperforming other types of compounds. In this work, we study structural and functional interactions in a technological system aimed at obtaining coatings by laser cladding of high-entropy materials, which are represented by the starting powders mixed in a certain proportion. The input and output parameters of the laser cladding process are established. This process is represented in the form of sequential phases, resulting in the formation of a coating on the surface of the product. The coating is characterized by both technological and specific properties, depending on the chemical composition of the starting powder components. A structural and functional scheme describing the process of coating formation from a high-entropy material during laser cladding is proposed. Connections between the input and output process parameters are demonstrated. These connections reflect the formation of specific coating properties in the process of laser cladding as a result of interaction of the powder material with the laser beam. It is noted that structural and functional schemes should be used when simulating technological processes based on mathematical models, taking the occurring transformations of substances into account.

This paper demonstrates the feasibility of producing thin-thin slabs from a wide range of aluminum alloys using the twin-roll casting method. In the course of the research, the design and technological solutions of the currently known methods of continuous casting and rolling of sheet metal products were analyzed. In a laboratory setup for strip metal casting, the physical and technological parameters (such as temperature, casting speed, and heat removal rate) were tested to ensure a stable process for the production of thin-thin slabs (1–5 mm) from the aluminum alloys under study. For the first time in the field of metallurgy, the improvement of twin-roll casting technology allowed the cast thin slabs from wide-range aluminum alloys, specifically EN2024 (D16) (≥ 130 °C) and EN7075 (B95) (≥ 160 °C), to be produced.

In the initial phase of the research, the impact of the heat removal rate from the solidifying metal on the primary structure of the cast blank was investigated. It is demonstrated that, irrespective of the cooling rate, the α‑phase serves as the basic structure that determines the mechanical characteristics of the metal in cast workpieces for all the studied aluminum alloys. It was demonstrated that as the cooling rate increases to a level characteristic of twin-roll casting, the α‑phase in cast slabs exhibits a more uniform fine-grained structure. In this case, the small inclusions of dispersed intermetallic and eutectic phases present in the structure of cast slabs are evenly distributed across their cross-sections. As is known, there is a hereditary phenomenon between the primary structure of cast slabs and the quality of the final metal product. This relationship was confirmed by the improved strength characteristics of strips obtained by rolling experimental slabs.

We study the material composition of a ferromagnesian oxidized nickel ore of the Serov deposit. According to the results of chemical analysis, it was found that the studied ore is poor in the nickel content. Note that magnesium and iron are present in the ore as macroimpurities. The main nickel-containing minerals are lizardite and clinochlore; smaller amounts of nickel are contained in talc. To determine the optimal technological parameters of heap leaching and reveal their correlation dependences, we use the mathematical method of data processing, namely, the Box–Wilson steep ascent method. Based on the results of leaching, we compute the values of the efficiency criterion and the variance of the efficiency criterion and deduce a regression equation for the description of the process of leaching. The adequacy of the regression equation is established by using the Fisher criterion.

The results of mathematical processing of the experimental data show that the concentration of sulfuric acid in the solution, the pause between irrigations, and the specific consumption of the leaching solution exert a significant effect on the efficiency of leaching in the stage of nickel extraction from 0–30%.

On the basis of computed values of the efficiency criterion, we determine the values of variable parameters for the second stage of determination of the optimal conditions of leaching guaranteeing the efficient ore opening in the stage of nickel extraction up to 30%.

Structure and mechanical property of mechanically alloyed granules of the Al–7.7Mn–3.1Cu (wt.%) alloy are studied after annealing in the temperature range of 250–450 °C and compaction at 400–450 °C. It is shown that a ball milling for 10 h provides for a formation of aluminum based supersaturated solid solution and Al₆Mn phase. Comparison of X‑ray structural data and differential thermal analysis and the change in granule hardness demonstrates the occurrence of recrystallization processes and decomposition of supersaturated solid solution with precipitation of Al₆Mn and CuAl₂ phases at heating. Compaction of granules at 400 °C provides a sample’s density of 2.87 g/sm³ and microhardness of 310±16 HV. Annealing of the compacts obtained at 400–450 °C leads to an increase in density and strength. Compaction at 450 °C increases the density of material to 3.01 g/sm³ and provides better mechanical properties according to compression tests results. The alloy exhibits yield strength of 910±10 MPa, ultimate tensile strength of 1060±20 MPa, deformation to failure of 0.9% at room temperature and an average value of yield strength of 287±20 MPa without microfailures after 40% of compression at 350 °C.

The study presents findings on the application of various beneficiation methods to low-grade hematite ores, originally characterized as a clay rock with an iron content of 17.2%. The study presents the mineralogical composition of the original ore and examines the effectiveness of different beneficiation techniques, including jigging, magnetic separation (after roasting with additives), and flotation. The results reveal that the simplest method, jigging, significantly enhances the iron content in the concentrate, achieving a total iron content of 50%. However, this outcome is heavily influenced by the size of hematite inclusions within the ore. Further refinement through additional beneficiation methods allows the total iron content in the concentrate to reach 60%.

The paper presents the findings of research on the production of wire from 850 and 585 platinum-based alloys intended for use in jewelry chains. The chemical compositions of two novel jewelry alloys of 585 platinum-containing modifying additives of rhodium and ruthenium are proposed and patented. An analysis was carried out to evaluate the existing section rolling and drawing schedules for the three platinum alloys to identify more efficient drafting methods, with a focus on reducing the labor intensity of metal deformation processes and minimizing the force parameters. A computer model of section rolling for the studied jewelry alloys, based on 850 and 585 platinum, was developed to analyze the shape variation and force parameters of the process and to propose a new deformation schedule for the studied alloys with the accepted reduction distribution per pass. The new deformation schedule was characterized by a more uniform reduction distribution per pass than that observed in the existing schedule, allowing the number of rolling passes to be reduced due to their redistribution. In order to determine the rolling force and to model the process, an approximation formula was used to calculate the time resistance, which is dependent on the total degree of compression. By using proprietary software and computer simulation, the parameters of wire drawing with a diameter of up to 0.25 mm from the studied alloys were calculated, which allowed the deformation and force parameters to be assessed when implementing the proposed drafting schedule. In addition, it was established that the drawing process exhibits a sufficiently high safety factor and low power consumption. It is therefore recommended that the process be subjected to industrial testing. The findings of this research can be recommended for improving the technology of wire manufacturing from the 850 and 585 platinum alloys intended for jewelry chains.